Bovine herpesvirus type 1 (BoHV-1) is a viral pathogen of cattle that can cause severe respiratory tract infections known as infectious bovine rhinotracheitis (IBR), abortion in pregnant cows. BoHV-1 is also a significant contributor to the development of Bovine respiratory disease complex (BRDC). BRDC is a multifactorial disease in cattle involving initial viral respiratory infection that may include BoHV-1, bovine respiratory syncytial virus (BRSV) and bovine viral diarrheal virus (BVDV) followed by secondary bacterial infection and severe bronchopneumonia. BRDC costs the US cattle industry alone more than $1 billion annually. The ability of BoHV-1 to immunosuppress infected cattle, to establish a lifelong latent infection in the trigeminal ganglia (TG) of infected animals, to reactivate from latency upon stress, and to be transported anterogradely from neuron cell bodies in the trigeminal ganglia to axon termini in the nasal and upper respiratory epithelium followed by replication in the upper respiratory tract predisposes the latently infected animals to BRDC. Therefore, BoHV-1 is considered to be an important initiator of BRDC.
Currently, the only vaccine allowed in EU countries against BoHV-1 is the entire gE-deleted BoHV-1 vaccine. By using the gE gene-deleted marker vaccine, BoHV-1 has largely been eradicated in a number of European countries. The gE-deleted vaccine vaccinated cattle can be differentiated from the wild type (wt) BoHV-1-infected cattle by various assays and, in the field, the gE-deleted BoHV-1 vaccine is being used in conjunction with a serological marker test marketed by IDEXX. Because the gE-deleted BoHV-1 vaccine is distinguishable from wild type BoHV-1, it is a “Differentiating Infected from Vaccinated Animals” (DIVA) vaccine. DIVA status for any BoHV-1 vaccine is important for the enforcement of BoHV-1 eradication program, and is necessary for marketing a BoHV-1 vaccine in Europe. As a result, the gE-deleted BoHV-1 vaccine is the only BoHV-1 vaccine marketed in Europe.
The inventors have developed a new BoHV-1 vaccine called the BoHV-1 tmv vaccine. Comparative tests indicate that the vaccine efficacy the BoHV-1 tmv is significantly better than the gE-deleted BoHV-1 vaccine. Tests also indicate that the IDEEX test that is currently used to distinguish gE-deleted vaccine vaccinated cattle from wild type (wt) BoHV-1-infected cattle is not suitable for distinguishing the BoHV-1 tmv-vaccinated calves from BoHV-1 wt-infected calves. This may be because BoHV-ltmv has a carboxy-terminal deletion of amino acids 452-575 but it retains approximately two-thirds of the gE coding region. Hence, amino acids 1-451 of gE, including the extracellular and transmembrane domains, are present in the inventors' BoHV-1 tmv vaccine. Therefore, a serological marker test that would distinguish the BoHV-ltmv vaccinated animals from the BoHV-1 wt infected animals is necessary before the improved BoHV-1 tmv vaccine can be introduced in the field.